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Pacific Salmon: The Pink Peril

Pink salmon are being caught all over the UKImage source: Shutterstock

If there’s one thing that’s guaranteed to make most conservation-minded anglers’ blood run cold, it’s the idea of yet another invasive non-native species coming to join the Himalayan balsam, floating pennywort, American signal crayfish, Ponto-Caspian shrimp, and other unwelcome visitors which are already wreaking havoc on our rivers and lakes.

Yet that’s exactly what we’ve been seeing here in the British Isles this summer – with alien Pacific pink (or humpback) salmon showing up in unprecedented numbers in rivers around our coastline.

So why has this happened? And is there anything we do about it?

Far from home

An Alaskan pink salmon in its freshwater spawning phase.By Bering Land Bridge National Preserve – Pink Salmon, CC BY 2.0

As their name suggests, Pacific pink salmon (Oncorhynchus gorbusca) evolved in the rivers and seas of the northern Pacific rim, from Oregon all the way up to Alaska, and down the coast of Russia to the Korean peninsula.

Like the four other species of Pacific salmon – chum (dog), coho (silver), king (chinook) and sockeye (red) – they’re genetically programmed to thrive in hostile Arctic conditions without the beneficial warmth of the Gulf Stream.

Mature adult fish run into rivers in mid to late summer, spawn quickly, and die almost at once, boosting the rivers’ ecology with all the remaining marine nutrients in their bodies. The fry hatch within 80 days, and migrate to sea at a young age (unlike juvenile Atlantic salmon, which live in their rivers of birth for much longer).

Year classes are strongly defined in two-year cycles, and don’t mix at all – a characteristic which has led to some runs of Pacific salmon being completely obliterated by natural or man-made disasters. Maybe to make up for this, pinks are happy to stray some distance from their own rivers to colonise new water. But like so many other alien invaders, they’ve now moved far beyond their native range as a result of human intervention…

Starting in the 1960s, and continuing for about 40 years, it’s believed that Russian scientists started stocking them into the Barents and White seas with the intention of creating a commercial net fishery and canning industry.

From here, pink salmon started spreading to Finland and Norway (where breeding populations have become established) and then to Iceland, Denmark and Germany. Occasional two- to five-pounders have appeared in Scottish, Irish and English east coast rivers since the earliest years, but it’s the scale of this summer’s invasion which has started to cause concern.

What’s the problem?

Hundreds of pink salmon, from around two to five pounds, have been caught in more than 40 rivers around the British Isles in 2017 – from the Helmsdale and Ness to the Tyne, and even the Cong and Galway fisheries on Ireland’s River Corrib.

In England, they’ve turned up in Yorkshire’s Driffield West Beck, too, where David Southall was surprised to catch a hard-fighting 3lb specimen in August on a streamer intended for chalkstream trout.

Native Atlantic salmon are already under serious threat in most British rivers, and many anglers fear that a major influx of Pacific salmon could put them under even more pressure – either from competition, or via the introduction of pathogens and diseases still unknown.

Others argue that the earlier timing of pink salmon runs means that the adults will be long dead by the time our native salmon start trying to spawn, and any remaining redds are likely to be overcut. Juvenile pinks will migrate to sea much sooner, and at a far smaller size, than Atlantic salmon smolts, so it’s not so likely that significant competition will occur at this life stage either. Dying Pacific salmon could even contribute valuable nutrients to oligotrophic Scottish and Scandinavian catchments, making more food for Atlantic salmon parr.

Yet having said all this, if invasion ecology teaches us one thing, it’s that the potential for unintended consequences is almost limitless. So the wisest course is probably the precautionary approach.

More information is certainly needed, and fisheries scientists have already started researching the viability of pink salmon eggs in UK waters, by excavating redds in the River Ness and moving the eggs to incubation chambers for further observation. Empty egg shells were also recovered, suggesting that some alevins might already have hatched.

What else can we do?

In smaller rivers, controlling pink salmon by disturbing their very obvious redds might be an option, but in huge rivers like the Tay, this simply wouldn’t be possible, even in low summer water.

More than anything else, the UK’s fisheries authorities need information about this year’s pink salmon run, so they can prepare to deal with the next one (possibly even more numerous) in two years’ time (2019).

With their prominent hump, male pink salmon are very obvious, but some of the other differences from Atlantic salmon are more subtle. If you catch a small salmon at the back end of this season, and you suspect it might be a pink, here’s what to look out for:

Atlantic salmon

Pacific pink salmon

No spots on tail

Large black oval spots on tail

Pale mouth and tongue

Very dark mouth and tongue

Usually larger (up to 110cm in length)

Usually much smaller (40 – 60cm in length)

One or two spots on the gill cover, plus spots on the back above the lateral line

Steel-blue to blue-green back, silver flanks and white belly

Thicker base of tail than Pacific salmon

Breeding males have a distinctive humped back

If you think you’ve caught a pink salmon, here’s what to do:

Don’t return it to the water, but dispatch it humanely and report it to the relevant authorities (listed below) to arrange for inspection. If this isn’t possible, please retain some scale samples for further analysis.

England and Wales: Phone the Environment Agency on 0800 80 70 60.

Northern Ireland: Tag the fish and phone the Loughs Agency on +44 (0)28 71342100: replacement tags will be issued.

Scotland: Contact your local district fishery board and fishery trust: information will be collated by Fisheries Management Scotland and Marine Scotland Science.

About Theo Pike

Theo Pike is a freelance environmental, fishing and marketing writer. He’s Chair of Trustees of the South East Rivers Trust, and founding editor of urbantrout.net, a website and eco-brand dedicated to the urban fly fishing and river restoration movements.
His first book, Trout in Dirty Places, was published by Merlin Unwin Books in 2012, and his manual on controlling invasive non-native species, The Pocket Guide to Balsam Bashing, has recently been re-published in ebook format.
Theo now also works with the Wild Trout Trust as their Trout in the Town Officer (South) helping to boost the impact of this programme across the south of England and Wales.